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Ethylene Regulation of Tobacco Seedling Size, Floral Induction, and Subsequent Growth and Development¹

Tobacco (Nicotiana tabacum L.) seedlings in the starting bed may become too large for mechanical transplanting, especially during periods of rainy weather. Our objective was to hold the seedlings at a suitable size for transplanting without causing undesirable side effects. Ethephon (2-chloroethylphosphonic acid) was used temporarily stop growth of seedlings in conventional starting beds and in various controlled environments. Resumption of growth was dependent on dosage of the chemical. Growth was suppressed for about 10 days in seedlings that were sprayed, until wet, with 1,000 mg ethephon per liter of solution. Seedlings treated at that level resumed normal growth and development after transplanting to the field. Ethephon treatments during the pretransplant period did not affect yield of cured leaf except when the plants were exposed to a florally inductive environment immediately after the treatment. In that case, ethephon-treated plants flowered later and produced more leaves and higher yields than did nontreated plants. The seedlings were not responsive to a florally-lnductive environment during the period of growth suppression. Growth was temporarily suppressed in plants treated in the noninductive environments, but growth later resumed and yield and alkaloid content of those plants were comparable to nontreated plants transplanted at the optimal size. Use of the ethylene-releasing agent on rapidly growing tobacco seedlings in the starting bed offers the possibility of temporarily holding them at an optimal size without causing undesirable side-effects.

Key Words: Nicotiana tabacum L. • Tobacco culture • Growth regulators • Tobacco transplants

² Plant physiologist (also professor) and agronomist, respectively, Tobacco Physiology Laboratory, ARS, USDA and Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40506.

Received for publication July 18, 1977.